Gripper pads used in stretch wrap packaging machines such as found in U.S. Pat. No. 4,501,106 issued to Fritz F. Treiber et. al. on Feb. 26, 1985 were cemented on the underside of a fixed upper jaw of a film gripping device. They have been effective in performing their task of gripping and pulling the lead edge of film from a supply roll and maintaining their grip as underfolding of film occurred according to the description in the patent. The patent also discloses that the upper jaw includes thirteen fingers, each of which has its own individual pad cemented thereto. The actual number of fingers may vary, as determined by the machine design for a particular range of package sizes to be handled.
Although very effective in operation, the pads were subjected to wear and had to be replaced frequently, as often as every four to six weeks in instances of high machine usage. The location of the film gripping device in the machine in a rather tightly confined area and the fact that the pads were cemented to the undersides of the fingers necessitated that at least a portion of the film gripping device had to be removed from the machine, the pads scraped therefrom, the surfaces cleaned and new pads cemented in place of the old. This became a severe inconvenience for the machine owner if pad replacement was done on the spot, unless the unit was not needed for wrapping packages at the time and for any period thereafter for the cement to cure. The machine down-time problem was resolved in part by having the repairman carry replacement gripper assemblies with him. The repairman would remove and replace the assembly with a spare assembly, returning the worn one to the shop for installation of new pads and reuse on another machine. However, even such replacement could result in a machine down-time of from one to one and one-half hours. When occurring during the machine warranty period, the manufacturer would absorb the several hundred dollar cost of a service call. After expiration of the warranty period, this became a cost obligation of the machine owner, who not only had to absorb the cost of a service call, but also had to suffer the loss of wrapping productivity each time a gripping assembly required replacement. This presented still further machine operation problems, in that the time between servicing to correct gripper pad wear was often deliberately prolonged by the machine owner in order to minimize cost. This could cause poor film gripping, resulting in film pulling out of the gripping device prematurely. This, in turn, could cause an occasional package to be miswrapped, tripping package detectors to shut down the machine while the miswrapped package was removed. Removal of an improperly wrapped package could be easy or difficult, depending on several factors not requiring discussion here, but necessarily causing aggravation and further productivity loss.